Prime Minister Kevin Rudd's policy shift apparently damaged his credibility on tackling climate change, which could cost his party support in elections due by the end of the year, said Martin O'Shannessy, chief executive of the market research company Newspoll, which publishes the poll of the same name.

"The big leads that Labor had in managing the environment and managing climate change are disappearing," O'Shannessy told Sky News television on Tuesday.

Labor has led the conservative coalition in the respected Newspoll — which is produced every two weeks by the Sydney-based company part-owned by News Corp. — since before Rudd became his party's leader in December 2006.

He became prime minister in a crushing election victory a year later with a promise to cut Australia's carbon dioxide emissions by making major polluters pay for every ton of the climate-warming gas that they produce.

But with elections due late this year at a date yet to be set, Rudd announced last week that he had delayed plans to implement a carbon dioxide pollution reduction scheme that was to start in July 2011.

He blamed his decision on opposition obstruction in the Senate and the slow pace of other countries reaching an international agreement on cutting global emissions.

Commentators described the decision as Rudd's biggest policy backflip, since he had described climate change during his victorious 2007 election campaign as the greatest moral challenge facing Australians. A U.N. panel of scientists says greenhouse gases such as carbon dioxide — emitted mostly by burning fossil fuels for electricity and transportation — are causing climate change that threatens potentially catastrophic environmental damage such as floods, droughts and rising sea levels.

The Newspoll published in The Australian newspaper on Tuesday found that Labor's support has shrunk from 54 percent two weeks ago to 49 percent.

The conservative opposition coalition's support climbed 5 percentage points to a commanding 51 percent — the first time it had led Labor in Newspoll surveys since August 2006.

The latest Newspoll was based on a random national telephone survey at the weekend of 1,161 voters. It was a 3 percentage point margin of error.

Australia is one of the world's worst emitters per capita of greenhouse gases because of its heavy reliance on abundant reserves of coal for power generation. As the driest continent after Antarctica, it is also considered one of the most vulnerable countries to climate change.

Under the previous government, Australia and the United States were the only industrialized countries to refuse to ratify the United Nations' Kyoto Protocol on reducing carbon dioxide and other greenhouse gas emissions.